Three dimensional modelling apparatus

ABSTRACT

A system responsive to coordinate information for automatically providing a three-dimensional physical model of a desired geometry and comprising apparatus for selectably solidifying a solidifiable material on a sequential layer by layer basis characterized in that following selectable solidification of a given layer, the non-solidified portions thereof are removed and replaced by a removable support material which is not solidifiable under the same conditions as the solidifiable material.

FIELD OF THE INVENTION

The present invention relates to apparatus for three-dimensionalmodeling generally and more particularly to apparatus forthree-dimensional modeling in response to a computer output.

BACKGROUND OF THE INVENTION

Various systems for three dimensional modeling have been proposed. Thereis described in Hull U.S. Pat. No. 4,575,330 apparatus for production ofthree-dimensional objects by stereolithography. The system describedtherein is intended to produce a three-dimensional object from a fluidmedium capable of solidification when subjected to prescribedsynergistic stimulation and comprises apparatus for drawing upon andforming successive cross-sectional laminae of the object at atwo-dimensional interface and apparatus for moving the cross-sections asthey are formed and building up the object in step wise fashion, wherebya three-dimensional object is extracted from a substantiallytwo-dimensional surface.

An earlier publication by Hideo Kodama entitled "Automatic method forfabricating a three-dimensional plastic model with photo-hardeningpolymer", Rev. Sci. Instrum. 52(11) November, 1981, pp. 1770-1773describes many of the features appearing in the Hull Patent as well asadditional features.

An article by Alan J. Herbert entitled "Solid Object Generation" inJournal of Applied Photographic Engineering 8: 185-188 (1982) describesthe design of apparatus for producing a replica of a solid object usinga photopolymer.

FIG. 5 of the Hull Patent and FIGS. 1A and 1B of the Kodama articleillustrate layer by layer buildup of a model through radiation coupledto a solidifiable liquid through a mask using a "contact print"technique. Accordingly, the pattern mask for each layer must be in a 1:1scale relationship with the object to be generated and must be locatedextremely close to it.

A number of difficulties are involved in the use of a contact printtechnique due to the required 1:1 scale. If a complex object having atypical size of up to 10 inches on each side is contemplated andresolution of 100 microns is desired, approximately 2500 masks will berequired, covering an area of over 150 sq. meters. An extremely fastmechanism for moving and positioning the masks and the use ofnon-standard film of a given size for a given scale output would berequired.

The required proximity of the mask to the object in contact printexposure is not believed to be desirable in an industrial environmentbecause of anticipated contact between the mask and the solidifiableliquid due to vibrations in the liquid during positioning and movementof the masks and due to spurious impacts.

Neither Kodama nor Hull provides apparatus for accurate positioning ofthe mask and accurate registration of masks for different layers. Thepositioning error must not exceed the desired resolution, typically 100microns.

Both Kodama and the Hull patent employ an arrangement whereby the objectis built up onto a base which lies in a container of solidifiable liquidand moves with respect thereto. Such an arrangement involves placing abase displacement mechanism in the container and in contact with thesolidifiable liquid. Due to the high viscosity and glue-like nature ofsuch liquids, it is believed to be impractical to operate such a systemwhen it is desired to change materials in order to vary the mechanicalproperties or color of the object being generated. Neither Hull norKodama are suitable for use with highly viscous liquids.

Furthermore, should excessive radiation be applied to the liquid, theentire volume might solidify, thus encasing the support mechanismtherein.

Definition of the bottom limit of solidification for a given layer isachieved in the Hull and Kodama references by precise control ofirradiation energy levels. Due to the fact that energy intensitydecreases exponentially with depth within the liquid, this techniquedoes not provide a sharp definition in layer thickness, as noted by Hullon pages 9 and 10, referring to FIG. 4. Hull suggests solving theproblem of bottom limit definition by using an upwardly facing radiationtechnique which is not applicable to many geometrical configurations.

The prior art exemplified by the Kodama and Hull references does notprovide teaching of how to model various geometries which involvedifficulties, for example a closed internal cavity, such as a hollowball, isolated parts, such as a linked chain, and vertically concaveshapes, such as a simple water tap. The identification of situationswhich require the generation of support structures and the automaticgeneration of such structures are not suggested or obvious from theprior art. Neither Kodama nor Hull contain suggestions for maximizingutilization of the available model generation volume.

An additional difficulty involved in prior art modeling techniques ofthe type exemplified by the Kodama and Hull references, but which is notexplicitly considered by either is shrinkage of the solidifiable liquidduring solidification. Normal shrinkage for most of the available resinsemployed in the prior art is about 8% in volume and 2% in each lineardimension. This shrinkage can affect the dimensional accuracy of thethree dimensional model in the following principal ways: two-dimensionallinear scale changes, two-dimensional non-linear distortions due tointernal stresses with each individual layer as it solidifies andthree-dimensional distortions due to stresses arising from stresses inthe overall model during a final curing step.

The Hull technique suggests the use of direct laser writing in a vectormode, which requires extreme uniform writing speed in order to maintaina constant energy level and produce a uniform layer thickness andextremely sensitive resins.

SUMMARY OF THE INVENTION

The present invention seeks to provide three-dimensional modelingapparatus, which is fast, accurate and is suitable for use in anindustrial environment.

There is thus provided in accordance with a preferred embodiment of thepresent invention a system responsive to coordinate information forautomatically providing a three-dimensional physical model of a desiredgeometry and comprising apparatus for selectably solidifying asolidifiable material on a sequential layer by layer basis characterizedin that following selectable solidification of a given layer, thenon-solidified portions thereof are removed and replaced by a removablesupport material which is not solidifiable under the same conditions asthe solidifiable material. There is also provided in accordance with apreferred embodiment of the present invention a method responsive tocoordinate information for automatically providing a three-dimensionalphysical model of a desired geometry and comprising the step ofselectably solidifying a solidifiable material on a sequential layer bylayer basis characterized in that following selectable solidification ofa given layer, the non-solidified portions thereof are removed andreplaced by a removable support material which is not solidifiable underthe same conditions as the solidifiable material.

Additionally in accordance with a preferred embodiment of the presentinvention there is provided a system for automatically providing athree-dimensional physical model of a desired geometry and comprisingapparatus for sequentially irradiating a plurality of layers of asolidifiable liquid via erasable masks produced in accordance withreceived coordinate information.

Further in accordance with a preferred embodiment of the presentinvention there is provided a system for automatically providing athree-dimensional physical model of a desired geometry and comprisingapparatus for sequentially irradiating a plurality of layers of asolidifiable liquid via masks in a non-contacting proximity exposurewherein the masks are produced in accordance with received coordinateinformation, compensating for distortions resulting from the separationof the masks from the layers and the use of non-collimated illuminationin the non-contacting proximity exposure. Additionally in accordancewith a preferred embodiment of the invention there is provided a methodof automatically providing a three-dimensional physical model of adesired geometry and comprising the steps of sequentially irradiating aplurality of layers of a solidifiable liquid via erasable masks producedin accordance with received coordinate information.

Further in accordance with a preferred embodiment of the presentinvention there is provided a method for automatically providing athree-dimensional physical model of a desired geometry and comprisingthe steps of sequentially irradiating a plurality of layers of asolidifiable liquid via masks in a non-contacting proximity exposurewherein the masks are produced in accordance with received coordinateinformation, compensating for distortions resulting from the separationof the masks from the layers and the use of non-collimated illuminationin the non-contacting proximity exposure.

It is a particular feature of the present invention that the maskproduction with compensation can occur in real time or near real timeand is carried out preferably by a straightforward linear transformationof coordinates. Such a transformation can be carried out readily as partof a vector to raster conversion process which normally occurs inpreparation for three-dimensional modeling.

According to a further embodiment of the invention, exposure through theerasable mask may be line-by-line exposure using an electro-opticshutter, such as a light switching array, or frame-by-frame exposureusing a planar array such as an LCD array.

As an further alternative, the mask may be written directly onto thesurface of the solidifiable liquid as by an ink jet printer or plotter.

Further in accordance with a preferred embodiment of the presentinvention, the solidifiable liquid is formulated to have relativelysmall amounts of shrinkage.

According to a preferred embodiment of the invention, the active resinin the solidifiable liquid, which has a given shrinkage coefficient ismixed with another resin which has a given expansion coefficient inorder to provide a mixture which has a zero or near shrinkagecoefficient.

According to an alternative embodiment of the present invention,radiation of the liquid layer is carried out such that as shrinkageoccurs, additional solidifiable liquid moves into place to take up theshrinkage and is solidified, uniform thickness of the entire solidifiedportion of the solidifiable liquid layer being maintained.

According to a further alternative embodiment of the invention,radiation of the liquid layer may be patterned to restrict shrinkage atany given time to localized areas.

Additional apparatus and methods of modeling are also provided inaccordance with preferred embodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description, taken in conjunction with thedrawings in which:

FIGS. 1A and 1B are generalized block diagram illustrations of twoalternative embodiments of a three dimensional modeling systemconstructed and operative in accordance with a preferred embodiment ofthe present invention;

FIG. 1C is a pictorial illustration of proximity exposure employed,according to a preferred embodiment of the invention, in the apparatusof FIGS. 1A and 1B;

FIG. 2 is a cross sectional illustration of a hollow object formed inaccordance with the present invention and including liquid drainconduits formed therein;

FIG. 3 is a pictorial illustration of a complex object formed inaccordance with the present invention and including support legsintegrally formed therewith;

FIG. 4 is a pictorial illustration of two nested objects formed inaccordance with the present invention;

FIGS. 5A and 5B are illustrations of initially isolated parts of anobject during formation thereof in accordance with the present inventionand of the finished object respectively;

FIG. 6 is an illustration of a three-dimensional mapping and modelingtechnique employing a solid supporting material;

FIG. 7 illustrates a problem of spillover of solidifiable material;

FIG. 8 illustrates a technique for overcoming the problem of spilloverof solidifiable material;

FIG. 9 illustrates a section of a three-dimensional model formedaccording to an embodiment of the invention which overcomes the problemof spillover of solidifiable material;

FIG. 10 is a side sectional illustration of support elements joining athree-dimensional model to a surrounding enclosure in accordance with atechnique of the type shown in either of FIGS. 8 and 9;

FIG. 11 is a perspective view illustration of a material removalmechanism employing a fluid strip in accordance with an embodiment ofthe present invention;

FIG. 12 is an illustration of a technique for removal of non-polymerizedsolidifiable material in accordance with an embodiment of the presentinvention;

FIG. 13 is an illustration of a technique for solidification of residualnon-polymerized solidifiable material in accordance with an embodimentof the present invention;

FIG. 14 is an illustration of a technique of controlling the thicknessof a layer employing machining techniques;

FIG. 15 is an illustration of apparatus useful in the technique of FIG.14;

FIGS. 16A, 16B, 16C and 16D illustrate a technique for shrinkagecompensation employing radiation through complementary masks;

FIG. 17 is a side view pictorial illustration of apparatus for threedimensional modeling in accordance with an alternative embodiment of thepresent invention;

FIG. 18 is a side view pictorial illustration of a variation of theapparatus of FIG. 17;

FIG. 19 is a pictorial illustration of apparatus for direct exposureemploying an electro-optic shutter, which is useful in a direct exposuremodeling device according to the present invention;

FIG. 20 is a schematic representative of an imaging system employing apartially reflective mirror which is useful in the present invention;

FIG. 21 is a pictorial illustration of a three-dimensional modelassociated with utility elements in accordance with an embodiment of theinvention; and

FIG. 22 is a generalized illustration of a three-dimensional modelingsystem constructed and operative in accordance with a preferredembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference is now made to FIGS. 1A and 1B which generally illustrate twoalternative preferred embodiments of a three-dimensional modelinggenerator. The embodiment of FIG. 1A provides direct exposure of asolidifiable liquid, while the embodiment of FIG. 1B provides indirectexposure thereof.

Considering first the embodiment of FIG. 1A, there is seen an energysource 20, such as a laser or a strong arc lamp having a short gap,which provides a beam of radiation via a beam modulator and deflector30, which receives a data input from a data source 29. Data source 29may comprise any suitable data source and may comprise a computer aideddesign (CAD) system, a computerized tomograph (CT) scanner, a graphicworkstation, such as a PRISMA system manufactured by Scitex Corporationof Herzlia, Israel, or a digital terrain model (DTM), implemented in acartographic system such as an R280 system manufactured by ScitexCorporation.

The modulated and deflected beam impinges on a layer of a solidifiableliquid, lying in a solidification plane 23. The solidifiable liquid maybe any suitable radiation polymerizable material which is commonly usedin the coating and printing industries. Examples of such materials areas follows: 6180 of Vitralit, of Zurich, Switzerland, ELC 4480 ofElectro-lite Corporation of Danbury, Conn., U.S.A. and UVE-1014 ofGeneral Electric Company of Schenectady, N.Y., U.S.A.

The solidifiable layer is typically supported on a positioning mechanism26 and is associated with raw material and support material supplyapparatus 28 and layer fixing apparatus 30. A plurality of layersdefining a built up model 24 are selectably solidified on a sequentiallayer by layer basis wherein following selectable solidification of agiven layer, the non-solidified portions thereof are removed andreplaced by a removable support material which is not solidifiable underthe same conditions as the solidifiable material.

The data received by the beam deflector 30 may be of any suitable formand is typically in raster form, vector form, or a combination of both.When raster data is received, the beam is deflected across thesolidification plane so that it periodically sweeps the entire are ofthe layer in a dense and regular pattern, typically an arrangement ofdense parallel lines. This pattern may be realized by deflecting thebeam in a fast saw-tooth pattern in a first dimension, and in a slowsaw-tooth pattern in a perpendicular dimension. As the beam sweeps thesolidification plane, the data from the computer instructs the modulatorto switch the radiated energy on and off, so that whenever the beam isdirected to a location at which solidification is desired, the radiatedenergy is provided and whenever the beam is directed to a location atwhich solidification is not desired, the radiated energy is notprovided. A suitable beam deflector driver for use with raster data is ascanning mirror, such as model S-225-015-XLOB5 available from LincolnLaser Co. of Phoenix, Ariz., U.S.A.

When vector data is received, the beam is deflected to follow thedesired contours of the solid parts in the solidification plane and tofill in the area delimited thereby. A suitable beam deflector driver foruse with vector data may be found in galvanometric recordersmanufactured by Honeywell, Test Instrument Division, Denver, Colo.,U.S.A.

Considering now the indirect exposure embodiment of FIG. 1B, there isseen apparatus for producing graphic masks 32, typically including anenergy source 34, such as a small visible light laser source, such as alaser diode, a beam deflector and modulator 35 arranged to receive adata output from a computer or a storage medium, and a imaging mechanism36 which is operative to produce a graphic exposure mask 38 for eachlayer or group of layers of solidifiable liquid to be exposed, asappropriate.

The graphic exposure mask 38 is then exposed using a light source 40such as a Model AEL 1B, manufactured by Fusion UV Curing Systems ofRockville, Md., U.S.A. or alternatively any suitable collimated lightsource. Similarly to the embodiment of FIG. 1A, here the image of themask is projected onto a solidification plane 23 so as to selectablysolidify a layer of solidifiable layer.

The solidifiable layer is typically supported on a positioning mechanism26 and is associated with raw material and support material supplyapparatus 28 and layer fixing apparatus 30. A plurality of layers areselectably solidified on a sequential layer by layer basis whereinfollowing selectable solidification of a given layer, the non-solidifiedportions thereof are removed and replaced by a removable supportmaterial which is not solidifiable under the same conditions as thesolidifiable material.

In accordance with a preferred embodiment of the present invention,pre-processing of configuration information is provided in order toenable complex or hollow objects to be formed by the technique of thepresent invention.

In accordance with an embodiment of the invention, configurationinformation is received from a three dimensional CAD system, such as aUnigraphics system, manufactured by McAuto of St. Louis, Mo., U.S.A., inthe form a facet file, known as a geometry file generated by thesoftware package known by the tradename "Unipix". The apparatus of thepresent invention is operative to extract from the facet file,coordinate information in a layer by layer format.

In accordance with an alternative embodiment of the invention,conversion of data from a CAD format to a raster format may be achievedby requiring the CAD system to generate a sequence of parallel sectionsof the object, each spaced from the other by the desired resolution.Data for each such section is then converted into two dimensional rasterformat having the desired resolution. A stack of such sections defines athree dimensional matrix.

Sequential sectioning of three-dimensional objects is a conventionalcapability in CAD systems and is known as a "topographical map function"in the MEDUSA system available from Prime Computer, of Natick, Mass. Twodimensional conversion of CAD data into raster form is entirelyconventional and is commercially available in the Quantum 1 systemmanufactured by Scitex Corporation Ltd. of Herzlia, Israel, and is knowas the "plot" function in that system.

Reference is now made to FIG. 1C, which illustrates non-contactingproximity exposure which is employed in accordance with a preferredembodiment of the present invention. A light source 50 and associatedreflector 52, typically embodied in a Model AEL 1B, manufactured byFusion UV Curing Systems of Rockville, Md., U.S.A. emits a generallyconical beam 54 of of light within the UV band, which impinges on a mask56. Mask 56 typically comprises a transparent substrate 58, preferablyformed of glass on the underside of which is formed, as by xerographiccoating, a mask pattern 60.

The mask 56 is preferably spaced from the top surface of a solidifiablelayer 62 in order to prevent possible contamination of the mask 56 bythe solidifiable material. A preferred separation distance is between0.5 and 1.0 millimeter.

It is a particular feature of the present invention that theconfiguration and dimensions of mask pattern 60 are determined in orderto compensate for the distortions produced by the effect of theseparation of the mask 56 from the layer 62 under non-collimatedillustration.

Referring now to FIG. 2 there is seen a hollow object 100 constructed inaccordance with the present invention. In accordance with a preferredembodiment of the present invention, a drainage conduit 102 and an airconduit 103 are formed in the model as it is built up in order to permitdrainage of support material from the hollow region 104. The formationof such drainage conduits can take place in accordance with thefollowing sequence of operative steps:

1. Start examining a layer (the examined layer) at the top of the threedimensional matrix and begin to check each layer, layer by layer;

2. check whether the examined layer of the matrix is also the lowestlayer, if yes, go to step 9;

3. identify the areas in the examined layer having a zero binary value(this may be achieved using an algorithm available in the "clar"functionin the R-280 system of Scitex Corporation Ltd.);

4. check whether the zero areas in the examined layer overlap any zeroareas in the preceding layer that was checked;

5. if no, declare a new cavity and assign the non overlap zero areasthereto and proceed to step 2 for a subsequent layer lying below theprevious examined layer;

6. if yes, and if the zero area in the examined layer overlaps exactlyone zero area in the previous examined layer, assign it to the samecavity as that to which that zero area in the previous examined layer isassigned and proceed to step 2 for a subsequent layer lying below theprevious examined layer;

7. if yes, and if the zero area in the examined layer overlaps more thanone zero area in the previous examined layer, and all of the overlappedzero areas in the previous examined layer are assigned to the samecavity, then assign the zero area in the examined layer to the samecavity as that to which the overlapped zero areas in the previousexamined layer is assigned and proceed to step 2 for a subsequent layerlying below the previous examined layer;

8. if yes, and if the zero area in the examined layer overlaps more thanone zero area in the previous examined layer, and the overlapped zeroareas in the previous examined layer are assigned to different cavities,then assign the zero area in the examined layer and reassign all zeroareas communicating therewith in earlier examined layers to a singlecavity, discard the remaining cavity designations for the reassignedzero areas, and proceed to step 2 for a subsequent layer lying below theprevious examined layer;

9. once all of the layers of the matrix have been examined, determinethe minimum and maximum values of x, y and z of each cavity;

10. if any of these values lies at the periphery of the matrix, discardsuch cavity, as it is not isolated. All other cavities are considered tobe isolated;

11. for each isolated cavity choose x and y coordinates on the extremetop and bottom locations therein having respective highest and lowest zvalues;

12. for each cavity, assign zero values to locations having the same xand y coordinates as the top location or coordinates in the vicinitythereof and higher z values than the top location, thus defining aconduit;

13. for each cavity, assign zero values to locations having the same xand y coordinates as the bottom location or coordinates in the vicinitythereof and lower z values than the bottom location, thus defining aconduit;

14. optionally, the steps 12 and 13 may be terminated when the channelsdefined thereby communicate with a cavity which already has defined inassociation therewith conduits communicating with the periphery of thematrix.

15. Optionally, the channels may be blocked after drainage by filling orpartially filling them with solidifiable liquid and then solidifyingthem.

Reference is now made to FIG. 3, which illustrates an object constructedin accordance with the present invention and comprising mutuallyisolated parts 106 and 108. In accordance with an embodiment of thepresent invention, where a solid material is not employed, solid supportlegs 110 are generated to support the isolated parts on the floor of thecontainer or onto another part which is, itself, suitably supported. Thethickness of the support legs is preferably determined by the load to besupported thereby during modeling.

The formation of such support legs takes place in accordance with thefollowing sequence of operative steps:

1. Start examining a layer (the examined layer) at the top of the threedimensional matrix and begin to check each layer, layer by layer;

2. check whether the examined layer of the matrix is also the lowestlayer. If yes, go to step 9;

3. identify the areas in the examined layer having a unitary binaryvalue (one areas). (This may be achieved using an algorithm available inthe "clar" function in the R-280 system of Scitex Corporation Ltd.);

4. check whether the one areas in the examined layer overlap any oneareas in the preceding layer that was checked;

5. if no, declare a new part and assign the non overlap one areasthereto and proceed to step 2 for a subsequent layer lying below theprevious examined layer;

6. if yes, and if the one area in the examined layer overlaps exactlyone one area in the previous examined layer, assign it to the same partas that to which that one area in the previous examined layer isassigned and proceed to step 2 for a subsequent layer lying below theprevious examined layer;

7. if yes, and if the one area in the examined layer overlaps more thanone one area in the previous examined layer and all of the overlappedone areas in the previous examined layer are assigned to the same part,then assign the one area in the examined layer to the same part as thatto which the overlapped one areas in the previous examined layer areassigned and proceed to step 2 for a subsequent layer lying below theprevious examined layer;

8. if yes, and if the one area in the examined layer overlaps more thanone area in the previous examined layer, and the overlapped one areas inthe previous examined layer are assigned to different parts, then assignthe one area in the examined layer and reassign all one areascommunicating therewith in earlier examined layers to a single part,discard the remaining part designations for the reassigned one areas,and proceed to step 2 for a subsequent layer lying below the previouslyexamined layer;

9. once all of the layers of the matrix have been examined, determinethe minimum and maximum values of x, y and z for all of the parts;

10. if any of the values of minimum z equals one, then discard that partsince it lies on the bottom of the matrix and does not require support.Declare all remaining parts, "isolated parts";

11. for each isolated part determine four points with extreme x and ycoordinates. Preferably choose such locations having divergent x and yvalues, so as to provide wide support for the part;

12. for each part, assign one values to locations having the same x andy coordinates as the extreme locations or coordinates being within apredetermined range, such as 1 mm of the location coordinates of theextreme locations and lower z values than the extreme locations, thusdefining a plurality of support legs;

13. optionally, the steps 11 and 12 may be terminated when the supportlegs defined thereby engage a part which already has defined inassociation therewith conduits communicating with the periphery of thematrix.

Additionally in accordance with a preferred embodiment of the presentinvention, as seen in FIG. 4, a plurality of separate objects 112 and114 may be modeled together and placed with respect to each other sothat they do not touch, while at the same time, the plurality of objectsis mutually nested so as to occupy a minimum overall volume.

A technique for efficient nesting of a plurality of objects to bemodeled at the same time may take place in accordance with the followingsequence of operative steps:

1. For each of the objects to be modeled, determine the extremecoordinates and compute a minimum bounding volume in the form of a boxfor each such object;

2. sort the bounding volumes in decreasing order of volume;

3. define a three-dimensional raster matrix (master matrix) in which theobjects will be located;

4. place the biggest bounding volume in the matrix by copying thecontents of the matrix of that object into the master matrix, startingat location (1, 1, 1);

5. for each of the remaining bounding volumes, start with the nextbiggest volume and proceed one by one until the smallest volume isreached, in each case determine an orientation in the master matrix inwhich it can be placed without overlapping or touching any of thepreviously located bounding volumes, while causing no expansion or aminimal expansion of the originally selected master matrix definedvolume. In the course of fitting trails, the 6 possible orthogonalorientations may be tried;

6. when the best fit is found, place each of the remaining boundingvolumes in its best fit location;

7. the procedure for generating support legs described above inconnection with FIG. 6 may be employed to provide supports betweenadjacent non-touching objects. Any other suitable technique may also beemployed for this purpose.

Reference is now made to FIGS. 5A and 5B which illustrate the modelingof an object which includes initially isolated portions which are joinedas the model is built up from bottom to top. FIG. 5A shows the model atan intermediate stage having a portion 120 isolated from the mainportion 122, such that portion 120 requires support. FIG. 5B shows thecompleted model wherein the two portions have been joined such thatportion 120 does not require additional support.

If the support material is chosen to be a material which lacks therigidity to support portion 120, intermediate support may be realized byinitially identifying those portions which require intermediate supportand afterwards generating solid support legs, as described hereinabovein connection with FIG. 3.

The steps of identifying those portions which require support mayinclude the following sequence of operative steps:

1. Start examining a layer (the examined layer) at the bottom of thethree dimensional matrix and begin to check each layer, layer by layer;

2. identify the areas in the examined layer having a unitary binaryvalue (one areas). (This may be achieved using an algorithm available inthe "clar" function in the R-280 system of Scitex Corporation Ltd.);

3. check whether the one areas in the examined layer overlap any oneareas in the preceding layer that was checked;

4. if no, declare an isolated area and proceed with the following steps.If yes proceed to step 2 for the next layer;

5. generate a support for every isolated area, either by the techniquedescribed above in connection with FIG. 6 or by generating a mesh asfollows;

6. write from memory a two dimensional mesh matrix, typically lying in aplane parallel to the solidification plane and including lines of widthof the order of 1-3 voxels. The mesh is superimposed on the plane of theisolated area and joins the isolated area to the walls of the thecontainer and to stable objects therewithin. The mesh may readily beremoved when the model is completed.

Additionally in accordance with an embodiment of the invention,reference markings may be incorporated in the model by selectablychanging the coloring of the solidifiable liquid at predeterminedlayers.

Reference is not made to FIG. 6 which illustrates an alternativeembodiment of the invention wherein a solidifiable liquid layer 375 isprovided in a container 376 only at the solidification plane. Therebelowis disposed a support material 374, typically in solid form. In eachlayer, the polymerized resin is illustrated at reference numeral 372.The non-polymerized resin is removed from the non-polymerized regions ofeach layer which are then are filled with a support material 374, whichmay initially be in a liquid or paste form. Accordingly, the depth ofsolidification is determined by the thickness of the solidificationliquid layer 375. As a model 373 is built up (possibly in a container376), the height of the support material is increased accordingly suchthat it reaches to just below the solidification plane.

Solidification of the wax is preferably accelerated by application of acold plate in contact with the surface of layer 375. Alternatively anyother suitable technique for rapidly cooling the surface may beemployed.

The application of the support material 374 may be by spreading or byany other suitable technique. The support material can be allowed tosolidify. An example of a suitable solidifiable support material iscasting wax such as Cerita Filler Pattern Wax F 875, available from M.Argueso & Co., Inc. of Mamaroneck, N.Y., U.S.A. This wax may be appliedas a liquid at between 50 and 80 degrees centigrade and then be allowedto solidify at room temperature.

Upon completion of the model, the wax may be removed by melting, as itwill melt at about 60 degrees centigrade, while typical polymersemployed as solidifiable materials in the present invention canwithstand temperatures as high as 90 degrees centrigrade withoutdegradation. It is noted that heating of the wax causes expansionthereof, which could, in certain circumstances, damage the model.

According to the present invention, support materials other than wax maybe employed. One example of another suitable support material isexpandable polystyrene (EPS) which may be applied as a liquid, whichsolidifies into a rigid foam and which may be removed afterwards by useof suitable solvents such as acetone.

Melting of the wax may be achieved by heating in an oven. If it issought to use a microwave oven for this purpose, an additive, such aswater can be added to the wax to absorb microwave energy. An example ofa microwavable wax is 28-17 manufactured by M. Argueso & Co.

Alternatively, and particularly when expansion of the wax is notacceptable, the support material can be removed by rinsing with asolvent. If water is to be used as a solvent, the support material canbe Cerita Soluble Wax No 999, also available from M. Argueso & Co., Inc.

The use of a solid support material provides the possibility of modelingwithout the use of a container. A difficulty can be foreseen however,spillover of the solidifiable material, prior to hardening thereof. FIG.7 illustrates this anticipated problem and shows a layer 378 ofpolymerizable material, such as a resin, spread over previously formedlayers 382. Spillover is illustrated at reference numeral 380.

The problem of spillover can be eliminated by maintaining a peripheralbarrier around the exposure plane. According to a preferred embodimentof the present invention, the problem of spillover may be obviated asshown in FIG. 8. A boundary 388 is formed around the layer, as byphotopolymerization of a polymerizable material by exposure thereof tostrong UV light from a light source 384 via a mask 386, which definesthe boundary.

Separate exposure of the boundary using the apparatus shown in FIG. 8may be obviated, however, if the boundary is incorporated by themodeling software in the image data itself. FIG. 9 illustrates a layerproduced by such integrated modeling software including a object 392, aboundary 394 and support material 396.

Reference is now made to FIG. 10, which illustrates the use of the builtup boundary 402 to support a modeled body 398 by means of supportelements 400, which are generated integrally with boundary 402, which issupported in turn on a base 404.

Reference is now made to FIG. 11, which illustrates a preferredembodiment of apparatus for reclaiming of unsolidified solidifiablematerial 401. The apparatus comprises a "push-pull" fluid stripgenerator 403 including a "push" portion 405 having a fluid stream inlet407, coupled to a source of a pressurized fluid such as a gas, typicallyair, and defining an elongate nozzle 409. The "push" portion 405 isfixedly attached to a "pull" portion 411, having an elongate inletnozzle 413 which is arranged in spaced registration with nozzle 409which communicates with a fluid outlet 415 coupled to a vacuum source(not shown).

Operation of the fluid strip generator 403 provides a fluid conveyorwhich defines a fluid strip 417 between nozzles 409 and 413. The fluidstrip 413 draws unsolidified solidifiable material 401 from unexposedregions of a layer 419 and conveys the material 401 via nozzle 413 andoutlet 415 to a reclamation reservoir (not shown) or to a disposallocation. By providing relative movement between the layer 419 and thegenerator 403, substantially all of the unsolidified unsolidifiablematerial may be removed from layer 419 as a prelude to supply thereto ofsupport material.

Additionally in accordance with a preferred embodiment of the presentinvention, there is provided an alternative technique for removal ofunpolymerized solidifiable material without removing the solidifiedsupport material. FIG. 12 illustrates four typical stages in such atechnique. At stage 1, a resin is partially polymerized, as at 406, inaccordance with a predefined pattern, such that part of the resin, as at408, remains in a non-polymerized state.

At stage 2, a solvent 410, such as iso-propanol, is applied from adispenser 412. As seen at stage 3, a brush 414 may be employed formixing the solvent with the resin and thus producing a low viscosityfluid. At stage 4, a vacuum is applied, as via a conduit 416, to removethe low viscosity fluid.

It will be appreciated that notwithstanding the technique describedabove in connection with FIG. 12, a certain amount of residualunpolymerized resin remains, as indicated at reference numeral 420, inotherwise polymerized resin 418, shown in FIG. 13.

It may be desirable to fully cure the residual resin 418. FIG. 13 showsthree stages in a residual resin solidification technique. Stage A isthe stage prior to application of the technique of FIG. 12, while stageB illustrates the residual resin. According to a preferred embodiment ofthe present invention, the entire region containing the residualunpolymerized resin is flooded with UV radiation, thus polymerizing theresidual resin as illustrated at stage C of FIG. 13.

The foregoing technique of solidifying the residual unpolymerized resinprovides enhanced adhesion between layers at the expense of somewhatlower accuracy, which nevertheless is within acceptable limits.

In accordance with a preferred embodiment of the invention, it may bedesirable to control the thickness and flatness of a given layer of themodel. This may be accomplished advantageously by spreading a somewhatthicker layer of resin and support material and then mechanicalmachining subsequent to hardening of the solidifiable material and thesupport material. The use of such a technique may permit a much widertolerance in the thickness of application of application of the resinlayers.

Mechanical machining may also have the following operational advantages:Vertical accuracy; roughening the layer surface for better adhesion ofthe next layer; exposure of the polymer which had been covered with waxinadvertently; removal of the upper layer of the support material wax,which may contain oily components; removal of the top layer of thepolymerized material which may not be fully polymerized due to oxygeninhibition.

FIG. 14 illustrates the use of a single or multiple blade fly cutter 430to provide uniform thickness layers 426 and to remove excess material428. FIG. 15 illustrates a typical fly cutter 432 in operativeassociation with a layer surface 434. The use of a fly cutter 432 hasthe advantage that the net force applied to the workpiece at any giventime is almost negligible.

In accordance with the present invention, a problem of spatialdistortion due to shrinkage of the solidifiable material uponsolidification may be encountered. As noted above, such shrinkage may beas much as 2% in each linear dimension. According to one embodiment ofthe present invention, the problem of shrinkage may be overcome by usinga multiple step irradiation technique, wherein an initial irradiationtakes place followed by shrinkage. Excess solidifiable material tends tomove into the region vacated by the shrinkage.

A second irradiation step, typically in the same pattern as the firststep, takes place. Subsequent irradiation, hardening and filling incycles may also take place, as desired. The above technique forovercoming the shrinkage problem may also be carried out in a continuousmanner, by extending the duration of application of the radiation. Thistechnique is particularly useful in the present invention since, ascontrasted with the teachings of Kodama and Hull, the present inventionemploys a uniform support material which does not solidify in responseto radiation which solidifies the solidifiable material, and thus isimmune to undesired solidification due to non-uniform application orradiation.

According to an alternative embodiment of the present invention, anon-shrinking solidifiable liquid may be provided by mixing into theusual shrinking solidifiable liquid another liquid which expands uponsolidification by about the same amount that the shrinking solidifiableliquid shrinks. The ratio of the two components may be adjustedaccording to their shrinkage coefficients, so that the mixture has azero or near zero overall shrinkage coefficient. A typical resin thatexpands upon polymerization is Norbornene Spiroorthocarbonate, which ismentioned in the proceedings of RADCURE, 1984, at page 11-1. It may bemixed with epoxy-type photopolymers which have the usual shrinkagecoefficients of about 2%.

Distortions due to stresses in the model generated during a final curingstep may be avoided by eliminating the final curing step, which is madepossible by fully curing each layer as it is formed by overexposure ofeach solidification layer as it is formed. Such is not possible inaccordance with the Hull and Kodama teachings.

According to a further alternative embodiment of the present invention,the effects of shrinkage may be reduced by avoiding the simultaneousirradiation and solidification of large areas of the solidifiable layer.In this connection reference is made to FIGS. 16A-16D, which illustratetwo step irradiation of a given pattern in complementary checkerboardpatterns.

FIG. 16A shows a typical solidification pattern mask for a given layerof a model. In accordance with an embodiment of the invention, thispattern is broken down into two complementary typically checkerboardpattern masks, illustrated in FIGS. 16B and 16C. This pattern breakdownmay be realized either photographically, using appropriate screens orelectronically by logical AND operation between a mask pattern and adata pattern.

The solidifiable layer is exposed through each of the complementarypattern masks separately, such that distortions due to shrinkagefollowing the first exposure are at least partially compensated duringthe second exposure. If necessary, a third exposure may be carried outusing a mask which corresponds to the complete pattern or selectedportions thereof for filling in any unsolidified spaces in the pattern.The result of the complementary pattern exposure technique is asuperimposed solidified pattern as seen in FIG. 16D.

According to an alternative embodiment of the invention, the image canbe subdivided into localized regions by superimposing thereon a gridpattern. This grid pattern is preferably reoriented for each adjacentlayer.

According to a further alternative embodiment of the present invention,shrinkage compensation may be achieved by distorting the exposure masksthrough pre-processing so as to take into account expected shrinkage inthe finished model. Such a technique is employed in molding or castingwhen molds are distorted for such purpose.

According to an alternative embodiment of the invention, an image may begenerated on a transparent plate on a 1:1 or close to 1:1 scale by useof an ionographic electrophotographic method. This method may beimplemented using an ion deposition device such, as a model S3000available from Delphax Systems, Inc. of Toronoto, Canada, to charge anelectrostatic image on the bottom side of a transparent dielectricplate, such as glass or Plexiglass. As the plate is moved across thedevice, the image is developed in a single-component development device,such as in model S3000, mentioned above. The plate then carries a visualrepresentation of the image. The plate is then moved into place abovethe new layer, and serves as an exposure mask for a non-contact imagingprocess. After exposure, the plate is returned to the coating station,after having been cleaned and discharged.

Cleaning of the plate preferably takes place at the development station,so that almost all of the toner returns to the toner pool and can thusbe recycled.

Toner overflow can be compensated by decollimation. Inelectrophotography, it is known that while the location of the chargedimage on the dielectric medium is very accurate, the dry toner imagetends to overflow from the black areas into the white areas. It isproposed to control the degree of light-collimation so that the whiteareas will be enlarged on the account of the black areas to compensatefor toner overflow, thereby improving the accuracy of the image.

In order to transfer the image to a thick glass plate the plate shouldbe coated with a very thin layer of transparent conductor such as TinOxide superimposed by a layer of dielectric material such as mylar. Thedielectric material is charged by applying a high voltage to theconductive layer.

Reference is now made to FIG. 17, which illustrates an alternativeindirect exposure technique which differs from the apparatus andtechnique illustrated in FIG. 1B in that it eliminates the use ofphotographic film, which is somewhat expensive and replaces it by anerasable mask.

As seen in FIG. 17, the mask is typically formed on a glass substrate264 as by an electrophotographic technique. A desired pattern typicallyis generated on a charged electrophotographic drum 266 using a laserbeam from a laser source 268, passing through a beam modulator 270 andvia a scanning device 272, which causes the beam to write line by lineon the drum 266.

Rotation of the drum in a direction 274 causes the written surface ofthe drum 266 to receive toner on the written pattern from a reservoir276. The toner pattern is then contact transferred onto substrate 264and is subsequently fused thereon at a conventional fusing station 278.According to an alternative embodiment of the invention, the tonerpattern is not directly transferred from the drum to the substrates, butinstead one or more intermediate transfer cylinders are employed forthis purpose.

The patterned mask is conveyed into contact or near contact printingrelationship with the solidifiable layer 281 and flood exposed as by abright light source, such as a mercury vapor lamp 280.

After exposure, the substrate is rinsed, cleaned and dried at a cleaningstation 282 and recycled for re-use.

After transfer of the image to the substrate 264, the drum surface iscleaned by a cleaning blade 284 and is uniformly charged as by a coronadischarge device 286 before being written upon once again.

Advantages of the above-described embodiment include the ability toemploy flood exposure of the solidifiable layer while maintainingrelatively short exposure times without requiring highly sensitivephotopolymers or the use of expensive photographic film.

According to an alternative embodiment of the invention, the apparatusof FIG. 17 may employ a continuous band of mylar or other flexiblesubstrate instead of glass. Such an embodiment is illustrated in FIG.18, the same reference numerals being employed to designate equivalentelements to those in FIG. 17. The substrate may be reused oralternatively discarded after one or more use. Where disposable masksare employed, they may be produced by any suitable laser printer orplotter operating in a conventional mode.

Reference is now made to FIG. 19, which illustrates an alternativedirect exposure technique suitable for use in the apparatus of FIG. 1A.In the embodiment of FIG. 19, an elongate light source 288 is employedto illuminate a single line of voxels on the solidifiable layer via anelectronic line mask 290. The electronic line mask preferably comprisesa light switching array of Phillips, Valvo Division. Alternatively, themask may comprise a liquid crystal array, such as Datashow by Kodak, aPZT electro-optically switched array, or a mechanically operated linearmask.

Both the mask and the light source are translated in a direction 292across the solidifiable surface, by suitable one dimensional translationapparatus.

A technique employing the apparatus illustrated in FIG. 19 has theadvantage that it eliminates mask consumables.

It is appreciated that various small objects can be combined by suitablenesting techniques already discussed above so that they can be formedtogether in one building up process. Similarly, a large object may bebroken down into components, each of which may be made by the techniquesdescribed hereinabove.

According to an alternative embodiment of the present invention, desiredprojection of UV light may be achieved by using a special mirror whosereflectance can be modulated such that parts of its are reflective,while other parts are not. Such a reflective system can be found in aSoftplot 1221 Large Area Information Monochrome Display available fromGreyhawk systems, Inc. of Milpitas, Calif., U.S.A. A preferredconfiguration of projection apparatus is shown in FIG. 20.

Reference is now made to FIG. 21 which illustrates the association ofutility elements to generated three dimensional physical models. Suchelements may include a hanger 491 and indicia 493. Additionally aninternal communication conduit 495 may be formed within a physical model496. The model may be integrally formed with a removable externalcommunication port 497 for attachment of an external device to conduit495, such as for drainage of support material from an internal cavity inthe model. Once the port 497 is no longer needed, it may readily beseparated from the model. The same is true for elements 491 and 493. Thegeometrical definition of the utility elements is preferably stored inan appropriate library located in a computer memory such that theelements can be readily be called up and, scaled and oriented onto themodel as desired.

In accordance with a preferred embodiment of the invention, thetechniques and apparatus described herein may be employed in a negativemode in order to provide a model made out of support material which issurrounded by a relatively thin shell of solidified solidifiablematerial. This model can be readily employed as a pattern for investmentcasting of metals or other materials.

Reference is now made to FIG. 22, which illustrates a preferredembodiment of the system and method of the present invention andeffectively summarizes many of the teachings which appear hereinabove.

FIG. 22 illustrates a system 500 for producing three dimensionalphysical models which includes two basic subsystems, a mask producingsubsystem 502 and a physical model producing subsystem 504. The maskproducing subsystem preferably comprises inographic imaging apparatus506, including an ionographic writing head 508, such as a writingcartridge incorporated in a model 2460 graphic engine found in a modelS6000 printer, commercially available from Delphax Systems Corp. ofToronto, Canada.

Writing head 508 comprises an array of ion guns which produce a streamof ions in response to received control currents which are provided by agraphic engine 510, such as the 2460 graphic engine mentioned above.Graphic engine 510 is operative to convert graphic data received in aconventional graphic format to the control currents.

Writing head 508 writes onto a transparent dielectric surface 512 whichcoats a transparent conductive surface which is formed on the undersideof a transparent substrate 514, typically formed of glass. The substrate514 is typically supported on a carriage 513 which travels along alinear guide 516 transversely to writing head 508, which remainsstationary. The conductive surface and the dielectric surface arepreferably embodied in a commercially available film sold by HanitaCoatings of Hanita, Israel, and designated by Model No. HA 01215.

After ion deposition at writing head 508, the substrate 514 moves intooperative engagement with a developing unit 518, such as the developingunit incorporated as part of the aforementioned Model 2460 graphicengine. The developing unit 518 is operative to deposit toner onto theionized portions of the substrate 514 thereby generating a mask 515.

The mask producing subsystem 502 also comprises substrate cleaning andtoner removal apparatus 520 which removes the mask from the substrateafter use. Apparatus 520 may include and a brushing unit 521 and avacuum unit 522. A corona discharge device 523 electrically dischargesthe substrate after toner removal. Alternatively, the toner may beremoved magnetically even by a roller employed as part of the developingunit.

Following the developing of the latent ionographic image on thesubstrate 514, the substrate 514 leaves the mask producing subsystem 502and is transported to the physical model producing subsystem 504.

In the physical model producing subsystem 504, the mask bearingsubstrate is precisely positioned in operative engagement with anexposure unit 530, typically comprising a Model AEL1B UV light source,available from Fusion UV Curing Systems of Rockville, Md. U.S.A. Amechanical shutter 532 controls the exposure.

The three dimensional model is built up layer by layer on a modelsupport surface 534 which can be selectably positioned along the X and Zaxes by suitable conventional positioning apparatus 536. Initially themodel support surface 534 is located in operative engagement with andunder a resin applicator 540, such as a device identified by Part No.PN-650716 found in SNAH 88 of Nordson Corporation, Atlanta, Ga.

Applicator 540 receives a supply of resin from a reservoir 542 via avalve 544 and a supply pump 546 and is operative to provide a layer 550of resin onto support surface 534 which layer is of generally uniformthickness, typically 0.15 mm. Following application of a resin layerthereto, the surface 534 is positioned in operative engagement with, andunder exposure unit 530, such that the mask formed on substrate 514 liesintermediate the light source and the layer 550 in proximity to layer550 for proximity exposure as described above in connection with FIG.1C. The shutter 532 is opened for an appropriate duration, typically 5seconds, thus permitting exposure of the layer 550 through the mask 515and consequent hardening of the exposed regions of the layer 550. Theshutter is then closed.

The mask 515 together with its substrate 514 is returned to the maskproducing subsystem 502 for cleaning and preparation of a subsequentmask. In order to eliminate possible defects in the structure of themodel due to inherent defects in the transmissivity of the substrate,such as the presence of air bubbles, cracks scratches therein, theorientation of the substrate with respect to the ionographic imagingapparatus may be randomly varied for subsequent layers by changing therelative position of the latent image 515 on the substrate 514 andprecisely compensating for such variations at the exposure unit 530, inorder to preserve the registration of the layers of the model.Accordingly, the resulting defects do not occur at the same location ineach subsequent layer and thus their effect is negligible.

While a subsequent mask is being produced, the model generation processcontinues: the exposed layer 550 is positioned in operative engagementwith a fluid strip generator 560 for removal of unhardened resin fromlayer 550, as described hereinabove in connection with FIG. 11. Thegenerator 560 communicates with a "push-pull" fluid circulator 562,which may comprise one or more pumps to provide desired positive andnegative pressures. Generator 560 also communicates with a separator 564which separates non-solidified solidifiable material from the fluidstream and directs it to a reclamation reservoir 566.

The thus cleaned layer 550 is then transported into operative engagementwith a support material applicator unit 570 and associated reservoir572, valve 572 and pump 576, which may be similar in construction andoperation to units 540, 542, 544 and 546 but provide a support materialto fill in those regions in layer 550 from which the unsolidifiedsolidifiable material was removed. Preferably the support materialcomprises a melted wax of a type mentioned hereinabove. Unit 570provides a generally uniform top surface to layer 550.

After application of the melted wax to layer 550, the layer ispreferably transported into operative engagement with a cooling unit580, typically comprising a cooled plate 582, such as a block ofaluminum furnished with internal channels for the passage of a coolantfluid in communication with a cooled coolant fluid supply 584, such as aModel Coolflow CFT-33 commercially available from NESLAB InstrumentsInc., Portsmouth, N.H. U.S.A. Plate 582 is positioned as desired by apositioning mechanism 586. The wax is layer 550 is cooled by intimatecontact with cooled plate 582 in order to solidify it as quickly aspossible prior to further processing, as will be described hereinbelow.

Following solidification of the wax in layer 550, the layer istransported into operative engagement with a machining unit 590,typically comprising a conventional multi-blade fly cutter 592 driven bya motor 594 and associated with a dust collection hood 596 and vacuumcleaner 598. Machining unit 590 is operative to trim the top surface oflayer 550 to a precise, flat uniform thickness by removing, asappropriate, excessive thicknesses of both the solidified solidifiablematerial and the solidified support material.

It will be appreciated that the operation of the system for a singlelayer as described above is repeated multiple times, as the supportsurface 534 is lowered correspondingly, producing a multilayer built upmodel having precisely controlled dimensions.

It will be appreciated by persons skilled in the art that the presentinvention is not limited by what has been particularly shown anddescribed hereinabove. Rather the scope of the present invention isdefined only by the claims which follow:

We claim:
 1. A system for automatically providing a three-dimensionalphysical model of a desired geometry and comprising means forsequentially irradiating a plurality of layers of a solidifiablematerial via masks produced in accordance with received coordinateinformation, said masks comprising a reusable substrate, and means fordepositing toner on said reusable substrate in a first desired patternfor use as a first mask for exposure of one of said plurality of layersand for subsequently depositing toner on said reusable substrate in asecond desired pattern for use as a second mask for exposure of anotherof said plurality of layers.
 2. A system according to claim 1 andwherein said means for sequentially irradiating comprises anelectro-optic shutter.
 3. A system according to claim 1 and wherein saidsolidifiable liquid comprises an active resin having a given shrinkagecoefficient mixed with a second resin having a given expansioncoefficient in order to provide a mixture which has a zero or near zeroshrinkage coefficient.
 4. A system according to claim 1 and alsocomprising:means for providing coordinate information with respect to athree-dimensional element; means arranged to receive the coordinateinformation from the providing means and manipulate of the coordinateinformation so as to adapt it for use in three-dimensional modeling. 5.A system according to claim 4 and also comprising means for selectablyassociating stored shapes with said three dimensional model.
 6. A systemaccording to claim 1 and also comprising electrophotographic means fordepositing said toner.
 7. A system according to claim 1 and comprising amirror whose reflectance can be modulated in accordance with thecoordinate information such that parts of the mirror are reflective,while other parts are not, thereby providing selectable illumination ofsaid solidifiable material.
 8. A system according to claim 1 and alsocomprising means for mechanically machining the layers building up thephysical model.
 9. A system according to claim 8 and wherein said meansfor mechanically machining includes means for forming a level surface onsaid layers.
 10. A system according to claim 1 and also comprising meansfor selectably solidifying said solidifiable material comprisingmeansfor applying a solidifiable material onto a support in layers; andwherein said means for irradiating said solidifiable liquid includesmeans for irradiating said solidifiable material through multiple masks.11. A system according to claim 1 and comprising fluid strip generatingmeans for removal of non-solidified solidifiable material from saidlayer, thereby permitting reclamation of said non-solidifiedsolidifiable material.
 12. A system according to claim 1 and alsocomprising means for removal and reclamation of toner from said reusablesubstrate.
 13. A system according to claim 1 and wherein at least one ofsaid first and second desired patterns includes a superimposed gridpattern.
 14. A system for automatically providing a three-dimensionalphysical model of a desired geometry and comprising means forsequentially irradiating a plurality of layers of a solidifiablematerial via masks in a non-contacting proximity exposure wherein themasks are produced in accordance with received coordinate information,compensating for distortions resulting from the separation of the masksfrom the layers and the use of non-collimated illumination in thenon-contacting proximity exposure, said masks comprising a reusablesubstrate, means for depositing toner on said reusable substrate in afirst desired pattern for use as a first mask for exposure of one ofsaid plurality of layers and for subsequently depositing toner on saidreusable substrate in a second desired pattern for use as a second maskfor exposure of another of said plurality of layers.
 15. A method ofautomatically providing a three-dimensional physical model of a desiredgeometry and comprising the steps of sequentially irradiating aplurality of layers of a solidifiable material via masks produced inaccordance with received coordinate information, said steps ofsequentially irradiating comprising the steps of depositing toner on areusable substrate in a first desired pattern for use as a first maskfor exposure of one of said plurality of layers and subsequentlydepositing toner on said reusable substrate in a second desired patternfor use as a second mask for exposure of another of said plurality oflayers.
 16. A method according to claim 15 and also comprising the stepof exposure through the mask in a line-by-line manner.
 17. A methodaccording to claim 15 and comprising the step of irradiation ofsolidifiable material in a pattern such that as shrinkage occurs andadditional solidifiable material moves into place to take up theshrinkage and is solidified, uniform thickness of the entire solidifiedportion of the solidifiable liquid layer is maintained.
 18. A methodaccording to claim 15 and comprising the steps of irradiation ofsolidifiable material sequentially in complementary patterns.
 19. Amethod according to claim 15 and also comprising the steps of generatinga fluid strip in operative association with said layer for removal ofnon-solidified solidifiable material therefrom, thereby permittingreclamation of said non-solidified solidifiable material.
 20. A methodaccording to claim 15 and wherein said step of sequentially irradiatingcomprises the step of selecting the optical geometry to at leastpartially compensate for overflow of material used in generating themask, by deliberately enlarging a light source employed in saidirradiating step to enlarge the areas of said layer exposed through saidmask.
 21. A method according to claim 15 and also comprising the step ofremoving said toner from said reusable substrate following saidirradiating via the mask defined thereby.
 22. A method according toclaim 21 and also comprising the step of recycling said toner afterremoval thereof from said reusable substrate.
 23. A method according toclaim 15 and wherein said steps of sequentially irradiating alsocomprise the steps of randomly varying the relative location of thedeposition of toner on said reusable substrate, and compensating forsuch variations, whereby the effects of optical flaws in the reusablesubstrate will be lessened.
 24. A method for automatically providing athree-dimensional physical model of a desired geometry and comprisingthe steps of sequentially irradiating a plurality of layers of asolidifiable material via masks in a non-contacting proximity exposurewherein the masks are produced in accordance with received coordinateinformation, compensating for distortions resulting from the separationof the masks from the layers and the use of non-collimated illuminationin the non-contacting proximity exposure and compensating the masks fordistortions caused by separation of the masks from the layers and theuse of non-collimated illumination by means of the application of alinear transformation.
 25. A system according to claim 1 and whereinsaid means for depositing toner comprises an array of ion guns.
 26. Amethod of automatically providing a three-dimensional physical model ofa desired geometry comprising the following steps:sequentiallyirradiating a plurality of layers of a solidifiable material via masksproduced in accordance with received coordinate information, said stepsof sequentially irradiating comprising depositing of toner directly onone of said plurality of layers in a desired pattern for use as a maskfor exposure of said layer.
 27. A method according to claim 26 andwherein said step of depositing is carried out using an ink jet.
 28. Athree dimensional model constructed in accordance with a processincluding the following steps:sequentially irradiating a plurality oflayers of a solidifiable material via masks produced in accordance withreceived coordinate information, said steps of sequentially irradiatingcomprising the steps of depositing toner on a reusable substrate in afirst desired pattern for use as a first mask for exposure of one ofsaid plurality of layers and subsequently depositing toner on saidreusable substrate in a second desired pattern for use as a second maskfor exposure of another of said plurality of layers.